Methyl Bromide, the fumigant that is commonly used today around the world for killing soil pathogens, is being phased out from production and use by the year 2000 as it has been proven to destroy the ozone layer. Other fumigants currently available, such as Metam Sodium (sodium methyldithiocarbamate, Dazomet (mylone), and anhydrous ammonia have been found not to be as good as methyl bromide. These fumigants are water activated fumigants and require the presence of water to produce the necessary reaction and the production of the sterilizing fumigant gas.
Normally, when a water activated fumigant is injected into the ground and a plastic mulch is spread on this ground to hold the gases to kill the pathogens, this plastic prevents rain or irrigation water from entering the soil. If water enters the soil, this moisture does not evenly react with the water activated chemical. This is the main reason why these water activated chemicals have never worked as well as they should.
These water activated fumigants also require a certain soil temperature to activate the fumigant. In routine use, the farmer or grower applies these water activated fumigants and waits for rain or irrigation to activate the chemicals. Soil temperatures being unpredictable, these water-temperature-dependant chemicals perform unevenly and poorly. Uneven activation within the soil profile leaves some inactivated chemicals to persist. These inactivated chemicals are eventually activated during the growing season, but this erratic activation causes undesirable consequences such as killing or stunting of the desirable plants grown in the treated soil.